'Inadequate Damping' in the MOT

[Suitor_Stu]

Okay, so you may or may not remember my post a few weeks back here about MOTing a rough running bike, well I decided not to get it done till everything was running smoothly again and with a few things sorted she is now.

MOT is booked for Tuesday and I have gone over everything in one of the online MOT Manuals and I think the only thing I'm going to be close on is the possible inadequate damping of the front forks. They don't say in the manual what constitutes inadequate damping so was going to ask and see if anyone knows here?

Basically when I compress the front forks (rolling forward and braking hard with weight on front) they compress fine, but on the rebound they hit the top and bounce back down a couple of inches (roughly 2-3 and the forks are long) before the damping takes effect. As far as I can see there is no oil on the forks, but I may look a wee bit harder with directional light as the seals are kinda in the body-work. I remember someone telling me ages ago that you had something like a certain percentage of the fork that they could rebound on before it becomes a fail, but this may have just been tripe? My bike is an '96 Triumph Tiger which was fairly well renound for having spongy front suspension in the first place owing to it's 'big trailie' nature (I didn't compare what the rebound was like when I first got the bike tbh...)

Not that I can do much about it now (not enough time to change fork oil), but it would be nice to know seeing as I am needing to drive a couple hundred miles on tuesday afternoon and if the bike passed was planning on riding it instead of car.

Cheers,
Stu

[iooi]

A rough guide is if the car/bike bounces more that 2 or 3 times its going to fail.
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Just because my bike was A DIVVY, does not mean i am......

[smegballs]

I've had "slightly reduced damping effect" as an advisory on forks that were absolutley fucked. They had gaiters so no visible leakage so it was just the advisory.

Depends on how strict you mot'er is but as long as no oil is leaking I would hazard a guess and say they are likely to pass.

[Suitor_Stu]

[Walloper]

You'd be a fool to 'knowingly' ride a bike with gubbed shockers.

These little bits are fitted to the bike to allow the machine to accommodate unevenness of the road surface which permits greater control of the machine.
You risk getting chucked off or worse if you continue to use a bike with fcuked up suspension.

Have a bike shop check it out for you if you are in doubt.
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W-ireless A-rtificial L-ifeform L-imited to O-bservation P-eacekeeping and E-fficient R-epair

[temeluchus]

Id be tempted to change the oil in the forks. find what the stock oil weight is for the forks and fill with the next heaviest
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Some shite cruiser. Now with guns and FREEDOM!

[virus]

They'd have to be completely lacking in oil for a big trailie to fail on damping in my eyes, and you'd have to have a complete bastard of a tester to do so.

Take it down as it is, If it fails change the oil for the next grade up, as Temeluchus says, Ignore walloper, damping is overrated.



Cheers
John
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own: 81 xs1100g...
owned: 85 rat CG (sold), 91 GS500e (stolen), 84 gsx400f (scrapped), 81 z250 (siezed, siezed, scrapped), 83 cb250rs (sold), 84 gpz750r ratfighter (killed) 84gpz400 (sold), '80 cb650 ratfighter (wrote off) 95gsx6/12f ratfighter (killed) 91 xj900 (sold)
stinkwheel Well I just had my hands up a pigs fanny. Which makes your concerns pale into insignificance.

[chris-red]

[Suitor_Stu]

The front forks on this model are known to be fairly spongy and generally a bit crap anyway-and to be honest I only bought the bike in September (from the dealer I'm taking it to get an mot - it has had a service when there) and I haven't noticed any difference in handling when having a wee pre-mot shakedown. I only discovered this possible damping issue when going over the thing with a fine toothed comb and forcing the forks to compress before the mot, but as I said it could well have been like that before...

I'll see what they say tomorrow, if there's an advisory for it I'll def be doing something about it! I just don't have a yardstick, as it were, to judge what 'adequate damping' actually is...

[Walloper]

[el_oso]

use a bit of string like something (that doesn't fold up like string) and drop it down the fork leg to measure how much oil you have.

edit: something like a dip stick
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Duke 390
Previous: '05 XR125L | '96 XJ600S Diversion |'05 Suzuki GSXR1000 | '05 Honda CBR125-R | '97 YZF 600R Thundercat | '11 Honda CBR250
Car: Jeep Wrangler 4.0L

[Walloper]

[Suitor_Stu]

Cheers Walloper, but that's kinda the point - the model of my bike is known to have "colossal fork dive" when working 'well' and there is NO method to adjust the rates other than the good old fashioned way of stiffer springs or heavier fork oil.

Whilst I do take your point about riding something unsafe, I really don't feel that what I am experiencing is causing any real issue with the bike's handling (that is if there is even one, because not having seen another one of these bikes in the flesh let alone tested one side by side I can't tell if it's not just a quirk/feature of the shocking forks!), but I suppose that something like the damping rate, as you've explained it's is individual to every bike with every rider in every situation, so I guess I'll just have to see what an expert says on the matter after looking at my bike.

Cheers again
Stu

[Walloper]

All very trooo.

I assumed from the firt post you had no carnal knowledge of the beast so suggested you seek a Pro for advice.

I use a rule of thumb on matters such as this if in doubt check it out.
Asking bcf is not a bad place to start.

It would be a painfull flashback when your strapped up in A&E and you remember that niggle about was the suspension working properly or not.

My 'Big Trailie' was new from the factory but it made me seasick whenever I rode it. I fcuked about with the knob on the back spring for a day or so before I played with the dampening adjustment. Though the dealer 'ASSURED' me it was set properly. A mistake made asking the sales bod rather than a professional.

This is not exactly how a motorcycle 'shocker' works but it is a rough guide to the principles involved.
As the name suggests the dampener dampens the rate or speed at which the shocker moves.
Suspension Dampeners work by using the orifice effect of fluid/gas passing through a hole. Some dampeners use a single spring loaded poppet which will present a different 'orifice' to the fluid passing through a common hole in the system in both directions. The oil passes between both sides of the shocker through the orifice of the dampener.
The oil can pass through the centre, (i.e. A 1mm diameter hole) of the poppet in one direction. and/or unseat the poppet against the spring spring to flow around it passing through, effectively, a larger hole (i.e. A 2mm diameter).

This provides different dampening rated for the same closed system.

The adjustment of the dampener either acts on the spring to increase or decrease the tension/pressure acting on the poppet or the adjuster changes the size of the hole the fluid is passing through. It depends on what the OEM decides the system needs or what your pocket can afford.
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W-ireless A-rtificial L-ifeform L-imited to O-bservation P-eacekeeping and E-fficient R-epair

[Frost]

Is it possible that the fork seals are fucked, and either oil has escaped or someone has put insufficient oil in to reduce the pressure and seal weep giving insufficient damping?

Drain them completely, put in what the manual says and watch for leaking seals.

[smegballs]

Reading this has made me think that probably should do something about the rxs forks, the front brake just dives the forks rather than doing any stopping